For the last 20 years, a cultural movement and industry based on "happiness" has gained considerable traction in the United States. 

Book authors, corporate consultants and motivational speakers -- who claim to understand the secrets of happiness -- often show up in TED talks.

A new book by Smith College historian Daniel Horowitz called "Happier?" chronicles the rise of this field, known as "positive psychology."

Horowitz said it's a mix of neuroscience, eastern religion, evolutionary biology and behavioral economics.

Daniel Horowitz: It represents a shift in the field of psychology from mental illness, from anxiety and depression, to mental health, to subjective well-being-- and if we will, happiness. A slippery word, to be sure.

Karen Brown, NEPR: My sense is this is largely a white, middle-class movement of people who are looking to maximize their happiness in this particular way, and positive psychology. You think of -- to me, a higher income population. Is that true, and are those the people that need the most help with happiness?

Daniel Horowitz: The most interesting thing in the field, to me, is by and large, many scholars in the field don't want to talk about race, class, gender, sexuality. The evidence is abundant, although sometimes ambiguous, that poor people need more help in achieving happiness.

Clear from the research [is] that above a certain income level, additional income doesn't matter, but poverty is not a happy condition for most people in that state. ...